Excavation tools of the types described herein are typically mounted to conventional excavators of the type having a backhoe. The backhoe includes a dipper stick, and the tool is mounted on the outboard end of the dipper stick. The tools are employed for excavation of difficult-to-excavate intermediate substrate, e.g. substrate between the category of loose soil or loose gravel and the category of solid rock. Intermediate substrate requires special tools to be excavated efficiently. Loose soil or gravel can be excavated with a conventional bucket, but a conventional bucket is generally not effective in intermediate substrate. Solid rock excavation generally requires a hydraulic hammer, but a hydraulic hammer is not efficient for excavating intermediate substrate. Attempts have been made to develop tools that are effective and efficient in excavating intermediate substrate. Simply stated, there have been three general approaches, i.e. the single tooth approach; the added articulated tooth approach, in which a tooth is positioned behind the bucket; and the multi-tooth bucket approach, where several teeth are mounted on the back side of the bucket, e.g. as described in Arnold U.S. Pat. No. 4,279,085 and Arnold U.S. Pat. No. 4,457,085, the complete disclosures of each of which are incorporated herein by reference. Each of these approaches has been found to have drawbacks and none is efficient and effective for excavation of intermediate substrate.